(Swift 3,4,5...) Validate a JWS Using ECDSA P-521 SHA-512

Validates a JSON Web Signature (JWS) that uses ECDSA P-521 SHA-512

Note: This example requires Chilkat v9.5.0.66 or greater.

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func chilkatTest() {
    // This requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // Note: This example requires Chilkat v9.5.0.66 or greater.

    // This example takes a JSON signature in compact serialization format,
    // and uses an ECDSA public key to validate and recover the protected header and payload.

    // We only need a public key for signature validation.  This is the ECDSA public key
    // that is used:

    //      {"kty":"EC", 
    //       "crv":"P-521", 
    //       "x":"AekpBQ8ST8a8VcfVOTNl353vSrDCLLJXmPk06wTjxrrjcBpXp5EOnYG_NjFZ6OvLFV1jSfS9tsz4qUxcWceqwQGk", 
    //       "y":"ADSmRA43Z1DSNx_RvcLI87cdL07l6jQyyBXMoxVg_l2Th-x3S1WDhjDly79ajL4Kkd0AZMaZmh9ubmf63e3kyMj2" 
    //      } 

    let sbPubKey = CkoStringBuilder()!
    sbPubKey.append("{\"kty\":\"EC\",")
    sbPubKey.append("\"crv\":\"P-521\",")
    sbPubKey.append("\"x\":\"AekpBQ8ST8a8VcfVOTNl353vSrDCLLJXmPk06wTjxrrjcBpXp5EOnYG_NjFZ6OvLFV1jSfS9tsz4qUxcWceqwQGk\",")
    sbPubKey.append("\"y\":\"ADSmRA43Z1DSNx_RvcLI87cdL07l6jQyyBXMoxVg_l2Th-x3S1WDhjDly79ajL4Kkd0AZMaZmh9ubmf63e3kyMj2\"")
    sbPubKey.append("}")

    let pubKey = CkoPublicKey()!
    var success: Bool = pubKey.load(from: sbPubKey.getAsString())
    if success != true {
        print("\(pubKey.lastErrorText!)")
        return
    }

    let jws = CkoJws()!

    // Set the ECC public key:
    var signatureIndex: Int = 0
    jws.setPublicKey(signatureIndex, pubKey: pubKey)

    // Load the JWS.
    let sbJws = CkoStringBuilder()!
    sbJws.append("eyJhbGciOiJFUzUxMiJ9")
    sbJws.append(".")
    sbJws.append("UGF5bG9hZA")
    sbJws.append(".")
    sbJws.append("AdwMgeerwtHoh-l192l60hp9wAHZFVJbLfD_UxMi70cwnZOYaRI1bKPWROc-mZZq")
    sbJws.append("wqT2SI-KGDKB34XO0aw_7XdtAG8GaSwFKdCAPZgoXD2YBJZCPEX3xKpRwcdOO8Kp")
    sbJws.append("EHwJjyqOgzDO7iKvU8vcnwNrmxYbSW9ERBXukOXolLzeO_Jn")

    success = jws.loadSb(sbJws)
    if success != true {
        print("\(jws.lastErrorText!)")
        return
    }

    // Validate the 1st (and only) signature at index 0..
    var v: Int = jws.validate(signatureIndex).intValue
    if v < 0 {
        // Perhaps Chilkat was not unlocked or the trial expired..
        print("Method call failed for some other reason.")
        print("\(jws.lastErrorText!)")
        return
    }

    if v == 0 {
        print("Invalid signature.  The ECC key was incorrect, the JWS was invalid, or both.")
        return
    }

    // If we get here, the signature was validated..
    print("Signature validated.")
    print("--")

    // Recover the original content:
    print("Recovered content:")
    print("\(jws.getPayload("utf-8")!)")
    print("--")

    // Examine the protected header:
    var joseHeader: CkoJsonObject? = jws.getProtectedHeader(signatureIndex)
    if jws.lastMethodSuccess != true {
        print("No protected header found at the given index.")
        return
    }

    joseHeader.emitCompact = false

    print("Protected (JOSE) header:")
    print("\(joseHeader!.emit()!)")
    joseHeader = nil

    // Output:
    // (the string "Payload" was the content that was signed.)

    // 	Signature validated.
    // 	--
    // 	Recovered content:
    // 	Payload
    // 	--
    // 	Protected (JOSE) header:
    // 	{
    // 	  "alg": "ES512"
    // 	}

}